The invention is directed to a device for monitoring the functions of a plurality of control devices in a motor vehicle by means of a single monitoring indicator.
In vehicles commonly in use today a plurality of electronic control devices are usually provided which fulfill specific operating and safety functions in the operation of the vehicle. Such control devices serve e.g. to control and/or regulate the ignition, the fuel supply, the transmission, anti-skid means, power, exhaust gas, the braking process and the like. These control devices are commonly connected with one another via a common diagnostic bus at which a diagnostic connection is provided for checking the good working order of the control devices with a testing device. Further, the control devices can be connected with one another via a communications bus (e.g. CAN bus).
A monitoring indicator which is constructed e.g. as a monitoring light is assigned to every control device and lights up when there is an error in the associated control device. After the supply voltage is switched on, a so-called testing process takes place in every control device. This testing process switches on the monitoring light of every control device for the purpose of displaying the operability of every control device and its respective monitoring light. The testing process is terminated after a predetermined time period or at the occurrence of a determined event, e.g. when the engine is started. This test corresponds to the process presently used with other monitoring lights built into the dashboard, e.g. the oil indicator light. The expenditure on wiring is very high with this solution, particularly when a large number of control devices is provided. Further, a driver stage is required for every monitoring light, making the device costly.
It is further known to provide one monitoring light for a plurality of control devices, which monitoring light can be switched on by every control device. Again, this also requires a number of driver stages corresponding to the number of control devices. Above all, in a great number of control devices, synchronizing the individual test processes and control processes for the monitoring lights poses technical problems, is expensive and is hardly practical in terms of expenditure if there are more than two control devices. Moreover, with inadequate synchronization a flickering of the monitoring lights occurs during testing which impairs ease of monitoring.